Articles of footwear generally include two primary elements, an upper and a sole structure. The upper may be formed from a variety of material elements (e.g., textiles, polymer sheets, foam layers, leather, synthetic leather) that are stitched or bonded together to form a void for comfortably and securely receiving a foot. More particularly, the upper generally extends over the instep and toe areas of the foot, along the medial and lateral sides of the foot, under the foot, and around the heel area of the foot. In some articles of footwear, such as basketball shoes and boots, the upper may extend upward and around the ankle to provide support or protection for the ankle. Access to the void within the upper is generally provided by an ankle opening in a heel region of the footwear. A lacing system is often incorporated into the upper to adjust the fit of the upper, as well as permitting entry and removal of the foot from the void within the upper. In addition, the upper may include a tongue that extends under the lacing system to enhance adjustability and comfort of the footwear.
The sole structure is secured to a lower portion of the upper and is generally positioned between the foot and the ground. In many articles of footwear, including athletic footwear, the sole structure incorporates a sockliner, a midsole, and an outsole. The sockliner is a thin, compressible member located within the void (i.e., under the foot) to enhance footwear comfort. The midsole extends downward from the upper and forms a middle layer of the sole structure. In addition to attenuating ground reaction forces (i.e., providing cushioning for the foot), the midsole may limit foot motions or impart stability, for example. Although the midsole of athletic footwear may be primarily formed from a foamed polymer material, the midsole may include a variety of additional footwear elements that enhance the comfort or performance of the footwear, including plates, moderators, fluid-filled chambers, lasting elements, or motion control members. The outsole is secured to a lower surface of the midsole and forms a ground-contacting portion of the footwear. Additionally, the outsole may be formed from a durable and wear-resistant material that includes texturing to improve traction.